The present invention relates to cutting tools, more particularly to tools for countersinking, chamfering and deburring threaded holes.
When holes are threaded by a tap they are often rough at their entrances. Conventionally drill bits and the like are used as hole finishing tools to remove a small amount of material hence finishing the entrance of the hole. This process is known as chamfering or deburring. Drill bits have the disadvantage in that finishing a hole with them requires an additional operation, adding time and cost to complete a finished hole. In addition, drill bits often chatter as the chamfering is done. This chatter creates a roughness of its own at the entrance to the hole.
U.S. Pat. No. 3,233,260 discloses a technique for combining the operations of threading with a tap and deburring into a single operation. This technique has been successful only with straight fluted taps. Modern machining methods tend to use taps with helical flutes. Such taps offer certain benefit when tapping some kinds of materials and when tapping blind holes. The disadvantage has been that the combination hole finishing tools that have been available do not work on helical fluted taps. Deburring tools tend to bind, get stuck, and jam on the tap causing breakage of both cutting tools (the tap and the hole finishing tool) and in many instances when this happens damage to the work piece would also occur, possibly causing it to be scrapped. For this reason much time and effort has been taken to develop this invention to provide a reliable combined hole finishing tool for use on and in conjunction with helical fluted taps.